1. Field of the Invention
The present invention relates to an improvement in a frame structure for pivotably supporting a swing arm in a motorcycle or the like wherein an engine is mounted on a body frame having a front end provided with a head pipe for supporting a front suspension, and a swing arm for supporting a rear wheel is pivotably supported at its front end to the body frame at a rear portion thereof behind the engine.
2. Description of Background Art
FIG. 7 illustrates a conventional frame structure for pivotably supporting a swing arm. A pair of left and right pipes 41 are welded to a rear portion of a single main pipe 16' connected to a head pipe 15. A pair of left and right supporting plates 25' are welded both to a pair of left and right down tubes 17' connected to the head pipe 15 and to the pipes 41. A pivot shaft, not shown, for supporting a swing arm, not shown, is provided between the left and right supporting plates 25'.
According to the above conventional structure, the pair of pipes 41 are welded to the single main pipe 16', and the pair of supporting plates 25' are welded both to the pipes 41 and to the pair of down tubes 17'. Accordingly, the length of the welding is large to cause an increase in cost of construction. The shaft working for the connection of the swing arm to the pivot shaft extending between the supporting plates 25' is carried out after connecting all of the parts of the body frame. Accordingly, a unit to be handled in shaft working for the connection of the swing arm to the pivot shaft is large in size, so that the operation of the shaft provided for the connection of the swing arm is not easy.
In Japanese patent publication No. 3-24394 there is disclosed a swing arm supporting structure having a pair of left and right supporting plates connected by three cross members and a pivot shaft provided between the left and right supporting plates. This swing arm supporting structure is fixed to a pair of left and right main pipes and a pair of left and right down tubes. Accordingly, the number of parts is increased.